Vulcanization of rubber



Patented Dec. 5, 1944 a UNITED Company, Newark, N.

Jersey N0 Drawing.

This invention relates to rubber compositions containing amines. 'Inparticular, it! relatesto compositions prepared from natural rubber either crude, vulcanized :or reclaimed, an organic accelerator or accelerators of the carbon disulfide group, and one or more amines which may be aliphatic, aromatic, heterocyclio, or mixedalthough, as hereinafter pointed out, it is not entirely limited to the preparation of rubber com positions wherein carbon disulfide type accelerators are used.

A particular object of this invention is the production of vulcanized rubber products which have as herein disclosed, is attained without sacrifice of the other properties; hardness, elasticity, and

tear resistance, for example, are fully as good as, and in many instances better than,in products similarly made and composed but without amine.

Anotherobject of this invention is to improve the plasticity and workability of the unvulcanized rubber masses during mixing and milling, while largely or wholly eliminatingthe need for using degrading plasticizers such, as pine tar, asphalt, or oils. This feature is of most usein the handling of batches of rubber compositions intended forespecially tough products; in accordance with this invention, such batches are of good plasticity during milling and yet on vulcanization give products of the desired high toughness.

Other objects disclosure. i

These and other useful objects are attained by mixing together natural rubber, an organicac celerator, preferably of the-carbon disulfide group, and an amount of an amine which, when a carbon disulfide type accelerator i used, is in excess of that required to combine with the acidic, constituent or radical of the accelerator. Other usual compounding ,ingredients such as fillers,

will appear frornthe following vulcanizing agents, colorin materials, and antioxidants may be added to the mix, and the usual compounding, mixing, forming and vulcanizing technique followed as desired.

The carbon disulfide group of acceleratorsis (zinc dimethyl dithiocarbamate) Each molecule .5 made up of those accelerators which are deriva- Application November 22, 1941, Serial No. 420,100 I 'IClaincis. (01. 260-793) STATES PA sf Frederick C. Bersworth, Verona, N. J., and Morris Omansky, Brookline, Mass, assignors, by direct and mesne assignments, to The Martin Dennis J., a corporation of New of each a of these compounds contains atfleast one sulfurgroup which is capableof reacting with an aminogroup to form a quaternary ammonium salt or other reactionproduct Thusr -in mer= captobenzothiazole, the -'-SH group so reacts, iand in benzothiazyl disulfide both sulfur atoms of J the Se-S linkage so react. Hence substantiallyione mol of monoaminereacts with one mol of mer captobenzothiazole, while two mols ofua monoamine are required to react withpne mol-of benzothiazyl disulfide; When polyamines' aare used, the amount required tor'eact with the ace-*- celerator is less proportion to thenu'm'ber of amino groups-e; g. one-half mol of diarriine,or' one-third mol of triamineis substantially equiva f lent to one mol of monoamine. a"

The mere use of amines with carbon-disulfide type aoceleratorsinmaking rubber compositions,

with the amine presentin an amount.not'more than sufl'icient to combine' or react with thee'acw celerator, is not a feature of the present-ainven tion. Compositions so prepared: do not exhibit the rernarkableimprovement intensilestrength and toughness which is an outstanding feature of products made in accordance with'thisinvention,

wherein the amine is used in an amount fdefinitely l in excess of that required to combine or react .wll'l the accelerator. The amountofexcess amine will vary according to the composition-and thettype' of product desired. Excellent results are obtained with an excess of50, to 500 perjcentwof amine (basedon reactive molecular equivalentsqas, explained above). However, improvement. t -;in strength and toughness is apparent when an even smaller exces of amine isaused. Furthermore,

much larger quantities; of amines-roan, 5 e em: ployed, as in the production-of special, type .of

products. H

v 0 Most of the acidic accelerators in common .use

are of the carbon disulfidegroup.=;;Anyqother' acidic accelerators not of that group cangbe employed in the samexway-namely by using an ex? cess of amine over that necessary to neutralize the acidic constituents of the" accelerator simi amount of amine used is-Fsufiicient that the vulcanized product exhibits definitely improved toughness and tensile strength over a, product lacking such suflicient amount of; amine but otherwise identical. Q o Other accelerators than those of the ac1d1c type other Fatoms-fthanwcarbonand hydrogen.

may be used in carrying out this invention. However,- with such non-acidic, non-carbon disulfide group accelerators the improvements in toughness and tensile strength of the final product is more moderate for' thesame proportion of amine.

Amines *suitahle-v for disc in the present invention may be primary, secondary or tertiary, and

may be aliphatic, aromatic, heterocyclic (e. 1 g. piperizine) or mixed (e. g. benzyl amine), They lriethylene tetramineu polymethylene diamines. .rllso-zincluded are the I include the alkylene polyamines, e. g.- ethylene diamine, the polyethylene polyamines, andcthe rubber-amine products described in. the copending application of Frederick'C, Berswort-hcmne 10f the present applicants), Serial N0.,420,101, filed November 22, 1941.

applicationfor example by heating together These .rubbereamines. may be prepared as described in the said coperrding A under appropriate conditions rubber and; an amine I I ioiform-ailiquidproductwhichissoluble in water,

acids, landin -alkalies. As :statedin said .00- pending application, the rubberrused .in making such rubber-amine reaction products may, lbe either matural rubber, either as ciude rubber .or modified-eel g. :reclaimed, vulcanized :or chlorinatedend ;1-in,= or made from any of the usual formsrsuchcas pale crepe, smoked sheets, orlatex; inrit may" be ::a vulcanizable synthetic rubberlike polymer such "as a chloroprene polymer, a butardienerpolymenor an 'organicpolysulfide polymer. Elle-lamina:iskcharacterized byhaving per molepulezatfleastonesaminofnitrogen atom, eachlsuch aminoinitrogen atom lbei-ng attached to no other atomsdahanrcarbon:andlhydrogen, each such carbon atom to which'fthe amino nitrogen is attachedibbeingrnoniaromatic= (i.--e. not part of an aromatic .iring) rand also vbei-ng attached \to no The rubber and amine are "heated togetheruntil a water miscible rliquid productais produced, and

the amount of; amine usedlis .inexcess of-that. re- ;quiretl 'to' produce said :liquid product.

- procedure :of this invention, :the amines do mot serve as: accelerators, although they gen- 'erally' enhance the accelerating: action of the ac.- ce'lerators present. "Hence-{the customarily used secondary accelerators "or :activators such as diphenyl guanidine mayaxbe omitted from the mix,

in most instancesaat' least, when carryingout this 7 I invention. fffisueh activators are used, vulcanization times -and/ortemperatures will ordinarily-require reduction'accordingly.

, "In carrying outtheprocedure of TthlS invention,

therubber;accel-era'tor, and .amine,:to ether'with such other compoundingingredients as may :be required, are rmixed together by. usual milling techniqueso that a homogeneous rubberi-m-assis fproduce'd. This'ls'sheetedioutiorrotherwise formed ornrianipulated,andthenizvulcanized if desired,

generailly fin accordance with the usual :procedure "for handling *the -particular type of rubber composition -inj--quest-ion-e. g. :as for making tires,

soles; rubberized ifabric, :or other rubber products,

as 'the case may I r 'various mouiflcations are-possible in carrying outthls-processcas will be explainedimorezf ully in connection with :the following eexamples, which are :to Eb'e cons'idered :as illustrative rrather than limiting.

Example I I 'lsoftgsport soleI'stocks were made up, by con- Attentional technique, "from the followin ingredients, parts beingby weight-stock A being-confvtenti'onal ,forthis type of ,product while stockB ulfur .fAltaxf accelerator is made in accordance with the present invention.

' u Stock A.

Antloxldant S 1lene; i ller' (aiorm of calcium silicate). Dlphenyl guanidine Samples of each stock in the form of sheets about 1 inch thick were vulcanized at various steam pressures for various times, and it was :.:found that-the'ibest products were obtained, for

each stock, at about 40 pounds steam for 10 minutes.

"Tensile tests were run in th same manner for eseveral Samples .of. each stock; out from sh'eets about 1 6 inch ,thick, vulcanized'il0 minutes at '40 pounds steam. Results of :these tests, 'averaged for the samples of each stock;- are tabulatedibelow:

, vulcanized products-from "therefore,

. show .superior strengthas compared with those from stock .A, which-is a good grade ,of stock: for

this ,use. ,In addition, vulcanized ,productsirom Example it Tire tread stocks'were made up; ,conventional technique, from the following ingredients, parts-being by weight. ,Stock Cris .a conventional high-test tire treadstock; stockslD, E and F are made ,in' accordance with the present invention.

' Stock C Lsml; Di ,StockE Sam;

Smokedsheetaloo 106 i 1160' f Oarbon'black- 45 45 45 -40 Zinc oxide.-. 1 E5,

Stearic acid Sul r Altax accelerat Antioxidantl Antox Propylene polyamineu Rubber polyamine.

- Antox' 'is an antioxidant which also has an activating e'fiect upon the'f-fAltaxF Propylene polyamine isya dimerizationproduct'of 1, 2 pro or dimethyl piperazine.

, 2,364,052 *pyle'ne diamirie formed withfloss of NHa, and presumably corresponding to the formula CH3 The rubber polyamine is a'yellow, viscous or jelly-like water-soluble re:- action product of crude natural rubber and an .alkylene polyamine made in accordance with the copending application hereinabove referred to."

Incorporation of the amineswhen carbon black is used in the stock may be in any desired manher during the milling, but as a general rule'the mixing is best accomplished by adding the amine at the same time that the carbon black is added-'- except in the 'case of the more volatile amines,

which arepreferablyadded late in the mixing." As in Example I, severaltests were made i-on each stock to ascertain what were substantially the best vulcanizing conditions. These were esabout 1 5 inchthick vulcanized under the preferred conditions for each as above set forth.

Results of these tests, averagedforthe samples of each stock, are tabulated below: l l

l Tensile stress, pounds per square inch Elongation, per cent 7 V w Stock 0 Stock D Stock E Stock F Tensile strength at break. 4, 500 5, 126 5, 363 5, 336 Elongation at break i r 2 per cent 645 620 645 a 630 The tensile testson the samples of stock C showfresults above the average for usualtire tread stocks; as already pointedrout, stock C. is. a

high-test stock. Even so, the tensile" tests on the samples of stocks D, E, and Ftshow a remark able improvement over those on stock C, giving results far above those obtainable withgany tire tread stocks of which we are aware.

As to characteristics other than tensile strength and modulus, the four stocks in this example are substantially the same, any diflferences being sentially as follows, on inch stock:

smekc "stockn StockE smear Time; minutesH io 10 i 7% Poundsofsteam 40 40 40 minor and generally in favor of products made from stocks D, E, and F. t

The advantages resulting from the application of this invention tothe preparation of tire treads are of particular significance. They permit the manufacture of tires of remarkably increased mileage and wearing qualities, and thus aid materially the conservation of rubber, which finds its principal use in tire manufacture. i

As shown in the composition for stock F, this g 3 invention" permits the use of somewhat less carbon black, thus allowing the jproduction 01 a stock which should resist flexing better than conventional stocks, because of decreased loading of the rubber. Also, lower sulfur content is possible, without sacrifice of quality, and as a consequence the final products have better aging properties: Other forms of natural rubber than smoked sheets-e. g; pale crepe and reclaim--may be used, as in usual rubber technology, in the practice of this invention.

Another advantage of using amines in accordance with this invention is manifestin the preparation of very tough stocks such as those for tire treads, as just described. Since the amineshave a plasticizing efiect on theunvulcanized product, theymake it possible to handle like normal compounds the batches for very tough products, thus permitting a combination of plasticity during tional technique, from the following, ingredients,

parts being by weight. v

Stock G Stock H Stock J Stock Smoked sheets; .100 100 100 :45 45- i 45 45 1 1 1 1 ur 2.75 2.75 2.75 2.75 Altax" accelerator.... 1 1 l l Benzyl amine l l 2 Piperazine hexahydrata. A 1 3 As in the previous examples, tests were made on each stock to ascertain what were substantially the best vulcanizing conditions. These were found tobe, on stock, about 10 minutes at 40 pounds for each of the foregoing stocks G 3 to K inclusive. r i

Tensile testswere run as in the preceding ,examples; results are tabulated below:

Tensile stress, pounds per square inch Elongation, per cent r Stock G Stock H Stock J Stock K 183 12s 184 272 221 286 288 423 347 388 432 605 473 659 633 874 "694 858 950 1, 243 1, 008 1, 204 l, 294 1, 637 1, 355 1,612 1, 726 2, 030 1, 679 2, 061) 2, 215 2, 519 2, 106 2, 611 2, 762 3, 033 2, 676 3, 203 3, 337 3, 671 3, 205 3, 775 3, 941 4,133 3, 717 4, 423 4, 602 650 ,727 4,347 5,101 Tensile strength at break. 4, 905 4, 441 5, 288 5, 210 Elongation at break I percent; 665 665 663 660 The four stocks in this example are essentially the same as conventional stock C, except forthe amines. Stocks Gand H illustrate the use of amines in an amount only slightly in excess of that required to react with or neutralize the "Altax; no significant increase in tensile strength and toughness is shown by the products of stock H, while'products of stock G although definitely improved, are not as, good as those of stocks D, E and F. In stock-H, the amine functions primarily as an activator for the Altax,

Tire :tread stocks were made up, by conven-' accen -2 .01 course intended to secure greater homogeneity in the final .mixture. ..In making the master batch, it is advantageous .to use amine and rubber i in the ratio of at least 1 to 10, by weight. In

are presentin sufficient. amounttoirnpart thedesired plasticity.

. :Formakin products such 'asthose described in .the foregoing examples, theamount of amine required is, as indicated. only a-relatively ,szmall per .cent .on .the weight -.of the rubber, and about .the same .as, Orsoniewhat ,greater than, the

. amount of ,acceleratorona weight basis. When using non-acidic organic accelerators, the amountofamineshould begreater than that required to activate acidic accelerators, in order thatthe improved toughness andstrength can be attained in the final vulcanized product. This same criterion mayin fact'be applied tether-determination of :the amount of amine "necessary. -whatever -ac-' celerator is used-including :those accelerators of the carbon disulfide group-if the operator prefers such a criterion to tho sealready given. Lack .of .conclusive knowledge of the reactions leading to, and theexact atomic structure of, vulcanized rubbercompositions makes it generally impractical to set forth precisely the reactions of the amines and the accelerators in the procedure of this invention; the reactions and results already set forth herein are demonstrable facts whereas the theoryunderlyingetherrn is vague. It follows, therefore, that determination of the amount of amine must, in practice, be on the basis of physical characteristics during and a-fter mixing and vulcanization. 1? 1 I When using polyamines such as those used in Examples I and II, for instance, we have obtained good results whenusing only A part of such polyamines to one part Altax and "100 parts rubber (i. e. of the amounts of amines shown in Example II), and also whenusing two parts of fact, we have obtained-some of the best results with ratios of amine to rubber'of 1 to 5 and 1 to 3,

by weight. While even higher amounts of amine can be used, they are apt to present some d'ifiiculties in thoroughincorporation of all the amine in the-rubber. .Master :batches :of amine and rubber in the ratio of 1 to .3 are rubbery :masses which, although stillsolid, are soft and somewhat tacky, and havea-slow cold flow.

These batches are in themselvesnew products,

" and may be used for purposes :other than as master "batches. This -invention,; in fact, includes generally rubber compositions containing both natural rubber and amines as :herein defined, :in which the rubber is 'present'inan amountgreater than that of the amine, by weight; And while the products of this-invention are especiallyavaluable in vulcanized condition, they may'also be used in; their unvulcanized condition.

We claim: i 1. The process which comprises mixing together, to form a vulcanizable rubber. product,

such polyamines to one part Altax and 100 parts rubber. This represents a good working range with such compositions for mostpurposes.

The amounts of other amines, e. g. monoamines, which are requiredcan be determined .in accordance with the preceding discussion. Larger or smaller amounts of amines, within the range re quired in this invention, may be used if desired, .as in the preparation of special products, and when the ingredients of the stock are used in considerably different amounts from those given in the-examples, and in preparing master batches, as described below. I

The well-known master batch procedure may be followed in carrying out this invention. In so 'doing, aminorproportion of the rubber is mixed with the amine, together with more or less of the other compounding ingredients as desired, and the vresultingmaster batch is thenfincorporated with the balanceof the rubberand the other inaredients such as thefillers. This procedure is rubber, by weight.

natural rubber, an organic accelerator containing no free amino groups, and an amount of .an alkylene polyamine which is between about 50% and about 500% in excess of that required to activate said accelerator, said accelerator being present in an amount-which is in the order of that normally used with said rubber for ;pr,eparing conventional vulcanized rubber products, said amine being present in anamount not morle than about 3 :parts'per hundred partsoi rubber, by weight. L a

2.. The process of claim 1 in which the rubber is crude unvulcanized natural rubber.

3. The process of claim 1; in which the accelerator is a member of the carbon disulfide group of accelerators.

"fore vulcanization natural rubber, an. organic accelerator containing no free amino groups, and

an alkylene polyamine, said amine being present in-an amount between about 50% and'about 500% in excess of that required to activate said accelerator but in an amount not greater than about 3 parts per hundred parts of rubber, by weight.

j 5. A vulcanized rubber product-comprising before vulcanization natural rubber, an organic accelerator selected from the carbondisulfide group of accelerators, and an alkylene polyamine, said amine being present in an amount betweenabout 50% and about 500% in excess of that requiredto neutralize said accelerator but .inan amount not greater than about '3 parts per hundred-partsaof 6. A product in accordance with claim 4 in which the rubber is .crude unvulcanized natural rubber.

7. A product in accordance .with claim .5 in which the rubber is :crudeunvulcanized natural rubber.

. FREDERICK C. BERSWORTH.

MORRISOMANSKY. 

